it was also done on several pro level bikes. i believe it was the late 80 or early 90s. they used a front down tube and a rear grip shift on the end of the drops (a la bar end)

from the sram site:

1988
In January, at the Long Beach Show, SRAM debuts its first product, the Grip Shift® DB road bike twist shifter. The DB debuted shifting a SH-TY-20 across a 10-speed free-wheel. In April, the CAT-1 was introduced for tribars and road bars.
Bob Mionske places fourth, riding the DB/CAT-1 in the road race at the Seoul Olympics. Scott Molina wins the Ironman Triathlon using DB/CAT-1. Sachs' first MTB components, called the Rival ATB groupset, are introduced. Grip Shift® equipped rider wins the Race Across America. Kenny Souza wins the world biathlon championships with CAT-1.

1989
SRAM introduces the CX road shifter. Cannondale specs the CX shifter on mountain bikes. Grip Shift equipped racers dominate U.S. Criterium events using the CX shifter.